/Engine/Plugins/Runtime/XRBase/Source/XRBase/Public/DefaultXRCamera.h
Optionally called byAPlayerControllerto apply the orientation of the headset to the PC's rotation. If this is not done then the PC will face differently than the camera, which might be good (depending on the game).
virtual void ApplyHMDRotation ( [APlayerController](API\Runtime\Engine\GameFramework\APlayerController) * PC, FRotator & ViewRotation )